It's hard to remember a better week in the theatre. Three top-notch productions; three totally different dramas; three surprises: the year is going out with an exhilarating demonstration of the vividness and variety of the British stage.

Distilled, unadorned, concentrated, Michael Grandage's production of King Lear remakes the idea of what Shakespeare's play can be. What it doesn't have is an absolute sense of wilderness: of everything abandoned, wide-open, lashed. What it gains is something extraordinary. The action is literally contained in the pale timber box of Christopher Oram's compelling, spare design, a visual suggestion of the "nothing" that is so central to the tragedy. A fine, evocative soundscape by Adam Cork creates battles and threats as a distant rumble, but on stage there's no bellowing or rushing. Restraint suggests the huge forces that are being held back, and restraint is the keynote of Derek Jacobi's exquisitely calibrated performance.

Jacobi begins with twinkling dignity, almost a touch of Santa Claus and a definite echo of the Prospero he played in Grandage's Tempest: he relinquishes power leaning on a staff. He steps delicately, precisely into madness, his low-level vehemence making evident how full this play is of curses. He creates an electric shock in the storm scene, by seeming to do less than expected: his imprecations to the elements are delivered in a level whisper, as if they are an internal affair, not a regal warning. He saves his big roars for the howls of his towering final scene, when he enters carrying the dead Cordelia, then sinks back into a soft register for the closing moments – and a long, expiring sigh.

These moments with Cordelia are more than usually moving because they have been so carefully prepared for: Pippa Bennett-Warner makes this potentially irritating, namby-pamby heroine into a persuasively candid presence. She has a cool counterfoil in Gina McKee, who is langorous, silky and unceasingly vigilant as Goneril: in the opening scene, she keeps her eyes trained on her younger sister, simply willing her to fail.

This is a production which has Grandage's trademark fleetness: one scene is constantly dovetailed into another; sometimes characters seem to meld. Oram's slatted boards – light streams through their cracks in the storm – are blotched with slurries of white paint, as of snow flakes. Both Ron Cook – a wispy Fool who wipes a tear away as Lear goes mad – and Gwilym Lee's Poor Tom have blanched, mottled make-up. At times their faces almost disappear into the background. As if to make a wallpaper of Fools.

The RSC has also taken off from tradition: its own. It has blasted away from niminy-piminy Victorian children's literature and into Dahlworld, where kids are urged to be naughty, schoolgirls are swung by their pigtails to the back of the stalls and boys exhale burps so gigantic that they propel themselves fluorescently around the stage.

Dahl's story of Matilda, the bookish prodigy considered a "jumped-up germ" by her spiv father and trollop mum, who takes on the fearsome headmistress (the school motto says "children are maggots") is staged with theatre-engulfing dynamism by Matthew Warchus. Dennis Kelly's script is sharp. The songs by habitually dark and casually dirty Tim Minchin are sometimes pipingly sweet, sometimes like a gameshow fanfare, sometimes rockingly audience-shaking: they catch sour, raucous and plaintive notes, and invite a Spartacus-style resistance among kids and audiences.

Nimble boys and girls with hair in bunches like gorse bushes spill through the action with individual ease (Misty May Tindall executes a particularly striking comic turn) and extraordinarily agile choreographed episodes: leaping from mat to wooden horse to mattress, pushing each other on the way. The leading children's parts – divided between several actors – were decided for the first night by drawing straws, but you'd have thought Kerry Ingram was meant all along: peaky-faced but decisive, spikily dancing in her over-sized sandals, silvery-voiced, she is completely uningratiating: clever rather than cute. She has the perfect adversary in Bertie Carvel, who executes a consummate variation on the pantomime dame. If anyone doubted that Carvel was one of the great acting hopes of the new generation, they can just stop wondering now. He has been quiet at the Royal Court, foppish at the National, musical at the Donmar and baroque at the Almeida. Here, with a bosom like a teatray, and a desperate spring in his step, he bounces villainously across the action: furling a ribbon like a whip, tucking his Olympic aspirations into his T-shirt, along with a tiny bit of loose flesh. He is, like Roald Dahl, a supreme example of the sublime malign.

At the National, the continually inventive Marianne Elliott brings a new generation of actors to Alan Ayckbourn's 1980 play Season's Greetings and reveals what could look like a closely observed but easy anti-tinsel satire as something funnier, more fundamental and bleaker. Jenna Russell's dipso wife is having "a little nosebleed" while she prepares the lamb. David Troughton's fearsome ex-security man, who has a knife in his sock and has given his great-niece a crossbow for Christmas, is picking the gory bits out of a much-repeated TV movie. Mark Gatiss, an incompetent doctor whose most violent action is plunging his fists into the pockets of his beige cardy, is assembling a doomed puppet show of the Three Little Pigs.

Ayckbourn lays out his store of stranded women, heart-dead men and would-be creatives with a surprising amount of pleats and tucks in his arguments. Wild farcical action is overlaid with some of the most desolate lines imaginable. Katherine Parkinson's despondent wife tries to revive her husband, conked out with drink in the armchair: flipping his unresponsive bulk forwards, back, on to the floor, around the room, over her pregnant body, she looks at him and proclaims: "I had to fight for this." Catherine Tate sashays enliveningly through the action, swishing her hair, elevating her silken negligeed bosom, on her way to a bunkup, leaving on the way a last plea to her unresponsive husband. Loneliness is brilliantly choreographed. Everyone has their moment of solitary hope; everyone is coralled together into a tiny crowd. As you are at Christmas. Season's greetings.